What's the harm in trying to contact aliens in space? Well, for one, if they're hostile, a cosmic call lets them know where we are. So it goes in the blockbuster film "Battleship," which opens in U.S. theaters Friday (May 18).

In the movie, researchers send signals into space that are received by members of an advanced alien civilization, who then mount an attack on our planet.

To date, scientists have not found clear evidence of life elsewhere in the universe, but the premise might not be that farfetched. In fact, renowned astrophysicist Stephen Hawking has warned that if aliens find their way to Earth, it may not be the friendly close encounter we want.

With "Battleship" setting sail this week, SPACE.com caught up with Seth Shostak, a senior astronomer at the non-profit Search for Extraterrestrial Intelligence (SETI) Institute in California, to talk about the new science fiction action film (which is based on the original Hasbro board game), whether he thinks hostile alien civilizations really exist, and what message he would send into the cosmos.

SPACE.com: You were a science consultant during the making of "Battleship," weren't you? What kinds of things did the filmmakers ask you to help them with?

Seth Shostak: That's true. They flew a couple of scientists down to talk to the director, writer and producer. They had specific questions that they wanted help with, so I was one of the consultants. One specific thing that I remember is they were looking for some reasons for aliens to come to Earth. What might entice them to come here?

In general, when moviemakers talk to scientists, they usually see them as a resource to solve particular technical problems or script problems for them. So, something like: what sort of weaponry would aliens be able to wield? [Gallery: Aliens Invade Earth in 'Battleship' Film]

SPACE.com: What did you think of the movie concept when you first heard about it?

Shostak: I played Battleship as a kid, but we didn't play it with pieces, we played it with paper and pencil, so it was kind of like Tic-Tac-Toe. But I did play Battleship, so I remember I had a certain sympathy for the idea. Also, it is somewhat reminiscent of the cat and mouse naval battles that took place during the Second World War, before you had long distance aircraft and long before satellites. You didn't know where the enemy was, so it added a certain amount of suspense, caginess and second-guessing to the whole business of naval engagement that's somewhat missing today.

SPACE.com: In the film, scientists send a signal to a habitable planet that seems like it may have been based on the exoplanet Gliese 581g. Do you have any insights into whether that was the case?

Shostak: I'm sure that's not an accident. Gliese 581g is a goldilocks planet, so it's somewhat similar to our own. But if it doesn't have liquid oceans, they probably don't have good vehicles for waging war from the oceans against the Navy.

There's still a lot of argument within the astronomical community about whether Gliese 581g even really exists. But if we assume it does, it's a planet in the habitable zone, and we don't know too many in the habitable zone yet. But, that could change rather quickly now. The Kepler telescope has now been in orbit for three years, which is the minimum time needed to find an Earth analog.

SPACE.com: If there are aliens out there, do you think they're hostile civilizations?

Shostak: I think there's a lot of intelligence out there, but that's just my guess. Question is: Are they peaceable or hostile? You could say that the peaceable ones are just going to stay at home and play with their Nintendos, so if you do meet any of them, they might be hostile. [10 Alien Encounters Debunked]

That's certainly the case when you think of explorers here on Earth. Explorers tend to be the aggressive types — why else would they risk scurvy, mutiny and other bad things to go out there? So, you could say that any aliens that are actually moving and interested in going somewhere are likely to be more aggressive. But who knows? There could be a vast Klingon population who just want to visit as many planets as possible.

Some people have said that if you broadcast signals, you might wreak havoc and destruction on our own world. Stephen Hawking has commented on it, and it's hard to argue against that. But it's also the case that we've been shouting into the jungle for a long time now — for about 70 years. Ever since the Second World War, we've had television and FM radio going into space. Those signals are weak, but any society that could come to Earth could probably pick them up, so in some sense, we could give away our location.

SPACE.com: So how believable is the premise that intelligent life forms could intercept signals from Earth?

Shostak: We've had deliberate transmissions from Earth in the past, so the movie's premise is not unbelievable. I don't know if it's believable that they'd come here and take on the U.S. Navy — that part is probably more for the fun of it, but there's no denying that signals could be picked up at any distance if you have a big enough receiver. If they're sufficiently advanced and have had radio for some time, they could pick up a whole bunch of stuff.

SPACE.com: This idea that maybe we shouldn't broadcast our location, just in case — is this something that's actively debated in the science community?

Shostak: I'm the chair of the International Academy of Astronautics, and we're trying to re-write protocols of what to do, but it's one of those very contentious things.

Some people think we shouldn't broadcast because it would be too dangerous, but to me, that seems like kind of a funny thing to do because that means if you went out into your backyard, aimed a dish at Alpha Centauri, and sent them your poetry, that you're somehow violating some international agreement and could be thrown in the clink. But the real reason why I think it's not necessarily relevant is because we have been, and will be, broadcasting.

Any society that could come here could pick up the lights from New York. What should we do about that? Should we darken New York from now until the last human expires? Would we want to turn off all the radars at JFK airport?

Shredders descend upon a ship in "Battleship."Credit: ILM/Universal Pictures

SPACE.com: So if you could send a message out into the cosmos, what would you say?

Shostak: Well, if I was going to be able to get an answer back, I would say something different than a one-way message. If I was going to send a one-way message, I'd just send the Google servers. I would just send the entire Internet, because they would be able to figure out some of it. We're able to decode languages from history when we have a lot of it, a big corpus of data.

But if it ever got to a point where you could get into a conversation and ask questions, my two have always been: do you have music and do you have religion?

I wouldn't ask about physics because we could eventually figure that out, but those two questions are things only they would know.

You can follow SPACE.com staff writer Denise Chow on Twitter @denisechow. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcomand on Facebook.